This invention relates to a fuel injector for an internal combustion engine. More particularly, this invention relates to an improved method and apparatus for atomizing the fuel expelled from a fuel injector.
Various types of fuel injectors are used in the fuel injection systems of internal combustion engines. One type of injector uses a solenoid armature located between the pole piece of the solenoid and a fixed valve seat to operate the valve member. Examples of such electromagnetic fuel injectors or solenoid controlled valve structures are described in U.S. Pat. Nos. 4,515,129 issued May 7, 1985 to Stettner and 4,572,436 issued Feb. 25, 1986 to Stettner et al., the disclosures of which are hereby incorporated by reference. The above identified patents show arrangements in which an armature/valve is biased to a normally closed position against a fixed valve seat by a spring member. The armature/valve is operable between a seated, sealing position against the valve seat and an open position against a pole piece of the solenoid for controlling fuel flow through a fuel injector port in the valve seat.
Another type of fuel injector, referred to as a poppet valve injector, uses a solenoid to open a valve which exposes the poppet to a high pressure blast of fuel. When the pressure differential across the valve member reaches a desired level, the valve member is displaced from a valve seat and the nozzle discharges fuel to an engine inlet port. One poppet type injector is described in U.S. Pat. No. 5,070,845 issued to Avdenko et al. the disclosure of which is hereby incorporated by reference.
With either type of fuel injector, it is desirable to have complete combustion of the fuel injected into the engine cylinder to increase the fuel efficiency of the engine and to decrease undesirable emissions. The more finely the fuel is atomized, i.e. the smaller the fuel droplets, the more complete the combustion. The typical atomization with current fuel injectors yields droplets of between 30 and 100 microns Sauter mean diameter (SMD), when the engine is cold. It is desirable to reduce the droplet size to ensure that complete combustion occurs when cold starting an engine. The present invention uses a blast of air to increase the atomization, i.e. to decrease the droplet size.
U.S. Pat. No. 5,711,281 issued to Lorraine discloses the use of air to assist in the atomization of fuel. However, in the Lorraine reference, the fuel is expelled from the injector in a stream and the air is used to atomize this stream of fuel. In a fuel injector which uses a poppet valve or director member mounted to a director plate, the fuel exits the injector after passing over the poppet valve or director member. When this occurs, the detachment of fuel causes the fuel to form an xe2x80x9conion skinxe2x80x9d pattern which is very unstable in the presence of air. This fuel condition is referred to as sheeted fuel. A fuel injector is needed which reduces the fuel droplet size in a sheeted spray of fuel which has been atomized by a director or poppet valve.
In fuel injectors which use directors or poppet valves, such injectors were designed in such a way to avoid placing surfaces downstream of the injection port to prevent the accumulation of fuel on those surfaces. The accumulation of fuel on surfaces downstream of the injection port dramatically affects combustion of the fuel. A fuel injector is needed which increases the atomization of fuel without allowing fuel to accumulate on surfaces downstream of the injection port.
The fuel injector of the present invention includes a director, such as a ball or other director member, mounted downstream of the fuel injection port. When the valve is actuated, fuel passes over the ball. The fuel adheres to the ball until it reaches the equator of the ball. At the equator, the fuel begins to separate from the ball and forms a sheeted, cone-shaped configuration. Typically this cone has sides which are 15 degrees from vertical.
When used with poppet valve injectors, the present invention preferably includes an air distribution manifold above the valve ball. Air from an air source, such as from the engine air intake manifold is introduced into the distribution manifold. The distribution manifold includes ports for introducing air into the air distribution chamber. Air travels through the air distribution chamber at preferably a ninety degree angle to the direction of fuel flow, although other angles will work. The air stream is directed just below the ball""s equator. We have found that air at 300 kPa flowing at 102 standard liters per minute achieves excellent atomization. This blast of air causes the sheeted fuel to atomize to a droplet size in the range of 3 to 6 microns SMD. The opening below the ball is on the order of 0.1 inches and has side walls which are forty-five degrees from vertical. The thickness of the air distribution chamber is on the order of 0.01 inches. With these dimensions, we have found that the pressure drop across the lower opening is sufficient to prevent the accumulation of fuel on the surfaces below the poppet valve ball.
When the invention is used with solenoid actuated fuel injectors, a director plate is mounted downstream of the valve and valve seat. A ball, or other director member, is mounted to the director plate on the downstream side of the director plate. An air housing carries air from an air source to an air blast chamber. The air blast chamber directs air at preferably a ninety degree angle to the sheeted fuel. The air is directed just below the equator of the ball. The blast of air causes the sheeted fuel to atomize more finely. Instead of using a ball, directors of other shapes could be used such as ground balls of various shapes and truncated cones.